Preheat the oven to 350 F.
Whisk together the flour, 1 cup of the oats, baking powder, baking soda, salt, and cinnamon in a small bowl and set aside.
In a large bowl, add the brown sugar, eggs, mashed bananas, butter or oil, milk, and vanilla and whisk or beat with an electric or stand mixer until fully combined.
Add the flour mixture to the egg mixture 1/2 cup at a time, beating continuously, until smooth, then stir in the chocolate chips.
Line 15 muffin tins with parchment baking cups and fill 3/4 of the way with the muffin mixture, then top with the remaining 2 tablespoons of oats.
Bake for 25 minutes at 350 F until a toothpick comes out clean.